PSI - Issue 29

Giovanni Pancani et al. / Procedia Structural Integrity 29 (2020) 149–156 Giovanni Pancani, Matteo Bigongiari/ Structural Integrity Procedia 00 (2019) 000 – 000

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buildings were only redesigned in part to be adapted to the newdefensive needs. The Verruca was a wa tchtower, in visua l rela tionship with a system of surrounding towers, and was fortified with the intention of resisting the typical assaults of theMiddle Ages, with high wa lls and crenellations, where theshootingunits were positioned; thebuilding itself, loca ted inside the fortress, which has a t least three construction phases, a ll from the medieval period, has openings on the second floor (from the inside it is visible the arrangement of accommodation for beams that suggest the presence of a floor wooden)made to hide inside anarcher andhis weapon: the windows are instead embrasures. It is likely tha t the medieval castle had several entrances positioned on several levels: the tower, locatedon the topof the mountain, founded directly on the rock, is accessed by climbing through the spurs through boulders which, a lthough ruined and eroded by time, reveal the presence of a staircase through a narrow passage: a transition to the fina l level of defenseas canbe found in manyof theTuscan castles [Francovich1991][Arrighetti 2018].

Fig. 5. Elevation map of theWest façade, useful to understand the wall’s deformation

The medieval fortress had wa lls surrounding the tower as quickly schematized in a Leonardo sketch: during the process of modernizing thedefenses, thewa lls of the fortress were rebuilt andprobably enlarged byadapting thewall sections to the resistancenecessary todeflect the blows of theartillery; only the portions ofmasonry around theaccess door and the crenella tion to the west are a ttributable to typical characteristics of the medieval period and can be considered part of the origina lwalls. The rest of thewalls is the result of an enlargement obtainedwith theconstruction of embankments. As is customary to expect from the enceinte of the fifteenth-century defenses, against them there was a system of barrel-vaultedga lleries, orthogonal to the direction of any artillery shots, as in part is still visible in the northern sector. Understanding the evolutionaryhistorical development of thewa lls of the fortress is important for analyzing its conservative-structural problems: the lack of roofing structures, or vaulted systems, with the exception of the rooms inside the towers andbastions still accessible, clearly reduces the possibility of encountering some types of damage as a result of static problems. Theconstruction techniques of the fortress walls are of very different types: in genera l, they canbedivided into twomacro sets, the first typical of the medieval period and a second of the modern expansion. The oldest structures have a greater a ttention to the processingof regular and homogeneous construction elements, while the portions of modern architecture have very irregular elements and the a lmost total absence of horizontal texture. Froma constructivepoint of view, therefore, themedievalwa lls in general as theywere built should present fewer structural problems. The stoneused for theconstruction of the walls is for the most part "Verrucana": a resistant metamorphic rock of sedimentary origin that was created in the whole southern part of the Apuan Alps. It must be considered that the regularity of the medieval textures, visible in the fortress, is distinctly different between the buildings, such as the portionof thewa ll of the tower still visible or the gabled building, and the enceinte, as can be seen around the door entrance or the crenella tion: it is possible to see the composition of thecore of thesewa lls in the graft with the south-west bastion. The presence of the corner walls of the tower suggests the arrangement of its plant on the top rock. The construction phases of the internal building suggest a seismic problem, since following the stra tigraphic interface lines it seems that a reversal actionof the side facade hasentered into action following thepush of the roof pitches. Such hypotheses could be verified through calculation methods of the kinematic mechanisms of the now "archaeological" structures of the site [Ga lassi et a l. 2018]. The masonry portions of the enceinte of the modernperiod have a very irregular wa ll texture, with stones of differentmaterial and size, which do not respect the